A histochemical study of extraneuronal accumulation of noradrenaline in the guinea-pig trachea.

1. Accumulation of noradrenaline in extraneuronal tissue of the guinea-pig trachea has been studied by the use of the fluorescence histochemical technique of Falck and Hillarp.2. After incubation in solutions of noradrenaline, fluorescence developed in cellular structures (tracheal smooth muscle, vascular smooth muscle and endothelium, fibroblasts and chondroblasts), in the intercellular matrix of the cartilage and throughout the loose connective tissue of the adventitia and submucosa.3. The effect of various experimental procedures on the development of this fluorescence has been examined i.e. incubation with noradrenaline at reduced temperature (0 degrees C), removal of fluorescence by washing with Krebs solution at 37 degrees C or 0 degrees C, incubation with phenoxybenzamine (10(-4)M) or metanephrine (10(-4)M).4. From these observations it has been concluded that noradrenaline accumulates in the trachea:(a) in cellular structures where it is firmly bound, i.e. not easily removed by washing at 0 degrees C, and where the accumulation is prevented by phenoxybenzamine, metanephrine or cold.(b) in the intercellular matrix of the cartilage where it is also firmly bound, but where the accumulation is not prevented by phenoxybenzamine, metanephrine or cold. This probably represents binding to sulphated mucopolysaccharides.(c) in the adventitia and submucosa where it is loosely bound and easily removed by washing.5. Some implications of these findings in pharmacological experiments with guinea-pig trachea are discussed.